Joe Leaphorn, the “Legendary Lieutenant” of the Navajo Tribal Police, may have retired. But mystery readers can be happy that his creator, 81 year-old Tony Hillerman, has not. “Shape Shifter” is the kind of first-rate thriller and engaging cultural travelogue readers have come to expect from him.

Save for service in the U.S. Army during World War II, where he was decorated with the Silver Star and the Purple Heart for combat service in Europe, Mr. Hillerman has spent his entire life in the American Southwest, which he brings to life with his skillfully drawn characters, his complex and compelling stories and his lyrical descriptions of the landscape.

Through 18 “Navajo novels,” Mr. Hillerman shows how American Indians, whites and the other groups living in the beautiful but sometimes harsh and unforgiving Four Corners area (where Arizona, New Mexico, Utah and Colorado come together) manage to live side by side, though not always without conflict or confusion, while answering to very different cultures and values.

Mr. Hillerman also shows how crime, on and off the reservation, must be dealt with locally through a bewildering array of law enforcement agencies from the Navajo Tribal Police, through local police and sheriff’s departments, and the FBI, which has jurisdiction over felonies on federal land.

Along with the cultural and law enforcement smorgasbords, Mr. Hillerman also gives us finely-drawn mysteries built around series characters that readers can identify with. Mr. Hillerman’s characters get older, grow, and evolve, just like real people do.

In “Shape Shifter” the recently-retired Leaphorn has taken to no longer solving crimes about as much as Mr. Hillerman likely would take to no longer telling stories. That is, he’s bored out of his tree.

So when another retired and bored cop colleague sends him a current photo from a glossy home magazine of a historic and valuable Navajo rug that supposedly burned up years ago at a crime scene, Leaphorn’s curiosity is in gear. As a result, he noses into a criminal hornet’s nest that will cost his colleague his life and put Leaphorn’s in jeopardy.

The retired Leaphorn has no badge and no client in this one. He carries “deputy cards” from several local jurisdictions, but these are more a matter of courtesy than legal jurisdiction. So Leaphorn is basically on his own hook. Not an amateur, for sure. But no longer a professional either. His motivation is curiosity about an inconsistency having to do with an old case and the fear that a murderer is at large, getting away with it, and likely to kill again if not stopped.

The novel’s title is taken from one of the names for Navajo witches. Sometimes called shape shifters (also sometimes skinwalkers or hand tremblers), the Navajo witch can assume many shapes, from human form to a wolf or an owl or whatever else it requires for its evil purposes. So too can the villain of this piece.

Leaphorn’s adversary, the human shape shifter Leaphorn must outwit and bring to justice, is a resourceful and vicious bad guy whose lucrative criminal career has left death in its wake over several decades and at least three countries. He’s had a long run of successfully covering his murders by, after a fashion, killing himself. Only to appear again and kill again as someone else. Even with a score card, it’s impossible to know who the players are until Leaphorn makes the identities quit changing by connecting all the dots.

There is more in this novel about the Navajo way than there has been in recent numbers. And Mr. Hillerman also introduces us to an engaging young Hmong tribesman, homesick for Laos and his native culture. But unlike writers ranging from Melville to John D. MacDonald, Mr. Hillerman doesn’t interrupt the flow of his story with asides ranging from paragraphs to pages. He seamlessly includes the cultural material along with the narration and dialogue of the story. It becomes part of and informs his stories.

Readers see a somewhat different Joe Leaphorn in “Shape Shifter” than the one we first encountered in “The Blessing Way” of 1970. He’s more Navajo, less secular than the young lieutenant of the earlier novels. Engaging in a common regret of men in their mid-fifties, Leaphorn wishes he had listened more to the stories the old people told in the hogans on winter evenings.

Other of Mr. Hillerman’s regular characters, Navajo Tribal Police Sergeant Jim Chee and his new bride, Bernadette Manuelito Chee, as well as Leaphorn’s new interest, Professor Louisa Bourbonette, have walk on roles in “Shift Changer.” Leaphorn’s late and beloved wife Emma is always just off stage and never far from Leaphorn’s mind. Regular readers of the series will enjoy encountering these characters, if only briefly. But this one is a Leaphorn novel.

“Shape Shifter” can be enjoyed by the first time Hillerman reader. For these people there’s the prospect of the long Hillerman backlist, promising more hours of reading pleasure. Regular Hillerman readers will enjoy another visit to the exciting and appealing universe Mr. Hillerman has created over the past 35 years.